"Mean Girls" is a smart little comedy that tries, within the limits of the teen-movie form, to say some real things about high school girls and the struggle for popularity. Screenwriter Tina Fey writes with wit and observation, and she has a strong advantage in Mark Waters, a director who knows comedy and knows how to build performances.

Here, Waters puts together a talented ensemble of young actors and then directs them in a way that emphasizes comic fluidity, flexibility and scale. It's no coincidence or lucky accident of casting that all the supporting performances go right to the edge of absurdity without crossing the line into random zaniness. As in "The House of Yes" and "Freaky Friday," Waters keeps it wild but real, and the result is not only a series of lively scenes but lively close-ups: The big-eyed, expressive performances are just fun to watch.

It could have been generic. Lindsay Lohan plays Cady, who moves with her former hippie parents from Africa to Illinois, having been home-schooled all her life. She immediately falls in with two kids from the art crowd, Janis (Lizzy Caplan) and her gay friend, Damian (Daniel Franzese), who are both intelligent and humane. But when the school's reigning social divas, known as "the Plastics," take an interest in her, Cady decides, with the encouragement of her arty friends, to hang out with them. Supposedly she's doing it in a spirit of investigation, but she's also being seduced.

High school is confusing and treacherous, but it's also training for real life. Spending time with the chief Plastic, Regina (Rachel McAdams), Cady finds herself both hating her and wanting her approval -- a new feeling for her, but actually a common human situation. Rachel McAdams brings glamour and magnetism to Regina, but also the right hint of comic distance. McAdams nails the laugh, for example, when Regina offers up this supposedly damning description of a former boyfriend: "All he cares about is school, and his Mom, and his friends."

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Lacey Chabert and Amanda Seyfield, as Regina's lieutenants, are also adroit. Seyfield has a great deadpan as the monumentally stupid Karen, and Chabert in the more substantial role of Gretchen -- sly but insecure, a born follower -- shows lots of skill and nuance. Typically in such films, the lead character is the most bland, the normal person who's there to respond to everybody else's eccentricities. That's pretty much the case here, but Lohan is sensitive and appealing, a solid locus for audience sympathy.

Fey's script is full of funny schoolgirl slang ("Shut up!") and caustic riffs on various high school types -- the long-suffering principal (Tim Meadows), the obtuse jocks and, best of all, the hygiene teacher, who keeps telling the kids that if they have sex, they'll die. Fey also includes that rare specimen, the cool teacher, and assigns that role to herself. She plays it well, with the amused, rueful aura many of the best high school teachers have -- an aura that comes of being young and thought old and of being lost and thought wise.

-- Advisory: This film contains sexual situations.

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